The determination of pH is one of the most common process chemical measurements today. pH is a measure of a relative amount of hydrogen and hydroxide ions in an aqueous solution. In fermentation and cell culture, one of the most critical process challenges is to maintain the optimal pH level. Fermentation processes utilize a live organism, such as a yeast, bacteria, or fungus strain to produce an active ingredient. Fermentation processes normally have a relatively short duration (2-7 days). Cell culture is a process in which a mammalian cell is grown to produce an active ingredient. The cell culture process typically takes somewhat longer (2-8 weeks).
One significant challenge for pH measurement in the fermentation and cell culture fields is the cleaning processes involved with the fermenter or bioreactor. Specifically, the fermenter or bioreactor must be sterilized prior to the beginning of either process to ensure against cross batch contamination or any unwanted growths. In addition, pH sensors typically undergo a two point calibration using buffer solutions. The residual buffer chemicals must be removed prior to the beginning of a fermentation or culture batch. Such cleaning can include steaming the fermenter or bioreactor as well as the pH sensor. Exposure to high temperatures, steam and rapid thermal shock can significantly affect the sensor's life.